GABAA-receptor-mediated inhibition of the delayed increase in intragastric pressure to stimulation of vagal afferent fibres in cats.

1. The possible involvement of gamma-aminobutyric acidA (GABAA)- and GABAB-receptors in the inhibitory effects of GABA on the delayed increase in intragastric pressure of the stomach to stimulation of vagal afferent fibres in cats was studied. 2. Cats were anaesthetized with pentobarbitone-gallamine and pretreated with hexamethonium. GABA inhibited the hexamethonium-resistant delayed contraction of the stomach in a dose-dependent manner. Such effects of GABA were antagonized by both bicuculline and picrotoxin. 3. Muscimol, a GABAA-receptor agonist, mimicked the inhibitory effects of GABA and the effects of muscimol were antagonized by bicuculline and picrotoxin. The ID50 of muscimol was 10 times less than that of GABA. 4. In contrast to muscimol, baclofen, a GABAB-receptor agonist did not mimic the inhibitory effects of GABA. 5. The present experiments demonstrate that GABAA-receptors are involved in the inhibitory action of GABA on the delayed contraction of the stomach to vagal afferent stimulation.